1. Technical Field
The present invention relates to a gas valve, and more particularly to a plug member of a gas valve.
2. Description of Related Art
Typically, a gas valve is mounted on a gas pipe to adjust a gas flow in the pipe. FIG. 1 shows a conventional gas valve, which has a valve body 1 and a plug member 2. The valve body 1 has an inlet 1a and a chamber. The plug member 2 is received in the chamber of the valve body 1 for rotation by control. The plug member 2 has an axial bore 2a, a large bore 2b, a small bore 2c, and an adjusting slot 2d. The axial bore 2a is in a center of the plug member 2 and extends in an axial direction. The large bore 2b, which has a greater diameter than the small bore 2c, extends in a radial direction of the plug member 2, and connects to the axial bore 2a. The adjusting slot 2d is on a surface of the plug member 2, and has an end connected to the large bore 2b. A depth and a width of the adjusting slot 2d gradually reduces from the end connected to the large bore 2b to the other. The small bore 2c is next to adjusting slot 2d and extends to the axial bore 2a. 
FIG. 1 shows that the gas valve is providing the maximum gas flow, in which the large bore 2b is right under the inlet 1a. As the plug member 2 is being turned clockwise, from 90° to 247°, the gas flow will gradually reduce because of the adjusting slot 2d. After 247°, the gas valve is shut until the small bore 2c goes to under the inlet 1a. It is clearly shown in FIG. 2 that the gas flow linearly reduces in the beginning, and has a sudden change in the section I. It is because of the gap between the small bore 2c and the adjusting slot 2d. In practice, the plug member 2 is lubricated for a smooth rotation. However, the lubricating oil will flow into the adjusting slot 2d from the end closer to the small bore 2c, and is accumulated at the end where the lubricating oil flows in. It will make a nonlinear change (the dot line of the section II) before the sudden change (section I).